Since $V_{\text {out }}=V_{B E 3}+V_T\left(R_2 / R_1\right) \ln n$, we must find convenient values of $n, R_1$, and $R_2$ such that $\left(R_2 / R_1\right) \ln n \approx 17.2$. If $n=31$, then $R_2 / R_1 \approx 5$, yielding the layout . Note that $R_1$ is placed in the middle to partially cancel the effect of gradients.

Now suppose we choose $n=25$, obtaining $R_2 / R_1=5.34$. Such a value cannot be accurately established by simply adjusting the dimensions of $R_2$ and $R_1$.